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M 2 has been claimed to posses three distinct stellar components that areenhanced in iron relative to each other. We use equivalent width measurementsfrom 14 red giant branch stars from which Yong et al. detect a $\sim$0.8 dexwide, trimodal iron distribution to redetermine the metallicity of the cluster.In contrast to Yong et al., which derive atmospheric parameters following onlythe classical spectroscopic approach, we perform the chemical analysis usingthree different methods to constrain effective temperatures and surfacegravities. When atmospheric parameters are derived spectroscopically, wemeasure a trimodal metallicity distribution, that well resembles that by Yonget al. We find that the metallicity distribution from Fe II lines stronglydiffers from the distribution obtained from Fe I features when photometricgravities are adopted. The Fe I distribution mimics the metallicitydistribution obtained using spectroscopic parameters, while the Fe II shows thepresence of only two stellar groups with metallicity [Fe/H]$\simeq$-1.5 and-1.1 dex, which are internally homogeneous in iron. This finding, when coupledwith the high-resolution photometric evidence, demonstrates that M 2 iscomposed by a dominant population ($\sim$99%) homogeneous in iron and aminority component ($\sim$1%) enriched in iron with respect to the main clusterpopulation.

The iron dispersion of the globular cluster M 2, revised